Device containing pyrotechnic material and method of manufacturing said device

ABSTRACT

The present invention relates to a device containing pyrotechnic material, having a housing surrounding the pyrotechnic material, the device being wherein the housing is formed entirely from glass and contains at least one metal duct having a spark gap or a heating wire.

1. The present invention relates to a device containing pyrotechnicmaterial, comprising a housing surrounding the pyrotechnic material, anda method of manufacturing the device. In particular, the inventionrelates to a gas generator for a safety arrangement in motor vehicles oran igniter for such a gas generator.

BACKGROUND OF THE INVENTION

2. The gas generators and igniters currently on the market generallyhave a housing of stainless steel, aluminum or plastic. In fact in theigniters for gas generators, a high expenditure is necessary in order toproduce these in a fluid-tight and gas-tight construction. In mostcases, the metal ducts for the connecting cables of the igniters arecast integral into a metal ring with glass and the metal ring isconnected by means of a welding process with the remaining housing partsof the igniter.

3. Even an employment of plastic housings can not always ensure thegas-tight and fluid-tight construction of the igniter. Owing to theplurality of the required process steps, the production of the knownigniters is additionally extremely cost-intensive.

SUMMARY OF THE INVENTION

4. The present invention provides a device containing pyrotechnicmaterial, in particular an igniter for a gas generator which isabsolutely gas-tight and fluid-tight, has a lower weight compared withthe known igniters and owing to the use of a continuous manufacturingprocess can be produced at a more favorable cost. According to theinvention, for this a device containing pyrotechnic material isprovided, comprising a housing surrounding the pyrotechnic material,which device is wherein the housing is formed from glass and contains atleast one metal duct with a heating wire or a spark gap.

5. The pyrotechnic material can be solid, liquid or gaseous. Preferablythe device is an igniter for a gas generator for use in a safety devicefor motor vehicles, which contains one or more heating wires or a sparkgap for igniting the pyrotechnic material. The pyrotechnic material cancomprise a primary charge and a booster charge. The primary charge takesup in an optimum manner the thermal energy arising through theactivation of the igniter by means of a current impulse and ignites thebooster charge. The booster charge provides the necessary amount ofenergy-rich hot particles to ignite the propellant usually contained inthe gas generator.

6. A particularly preferred embodiment of the device according to theinvention contains an arrangement by which in the case of an undesiredthermal action from the exterior, for example when the vehicle catchesfire, an opening is exposed and thereby a controlled outflow can beensured of the gas released by the self-ignition of the pyrotechnicmaterial. This arrangement preferably comprises a material which iscrystalline or liquid at room temperature and is introduced at asuitable point into the glass housing of the device. The crystalline orliquid material alters its structure, its physical condition or itsvolume below the self-ignition temperature of the pyrotechnic materialin such a way that when the undesired thermal action from the exterioroccurs, the arrangement exposes the opening in the housing of the devicewhich is closed by the arrangement.

7. The arrangement can comprise in particular an opening formed in theglass housing of the device, the opening being closed by a sealing meanswhich may be formed particularly preferably from a low-melting-pointmetal alloy. The sealing means may further be a liquid contained in aclosed glass container, the glass container being introduced in theopening and integrally connected with the glass housing.

8. The device according to the invention can also be a gas generator fora safety arrangement in vehicles, which generator can be used inparticular in belt tensioner units or airbag modules.

9. A further subject matter of the invention is a method ofmanufacturing a device containing a pyrotechnic material, the methodcomprising the following steps:

10. (a) providing a glass bulb having at least one opening;

11. (b) introducing the pyrotechnic material and the at least one metalduct with the spark gap or the heating wire into the glass bulb;

12. (c) closing the at least one opening of the glass bulb forming aglass housing completely surrounding the pyrotechnic material andcontaining the metal duct.

13. In a preferred embodiment of the method according to the invention,first the metal duct with the spark gap or the heating wire can beintroduced into the glass bulb through a first opening, the glass bulbcan be heated in the region of the metal duct up to softening of theglass material and be closed in a gas-tight and fluid-tight manner forexample by pressing or squeezing the softened glass. Glass bulbs havingmelted-in metal ducts and the associated heating wires or spark gaps mayalso be utilized in the form of already prefabricated units. Thereafter,the pyrotechnic material is introduced into the glass bulb through afurther opening and this opening is likewise closed in a gas-tight andfluid-tight manner. The closing may be done for example by sealinglymelting, pressing or squeezing. The glass bulb is preferably heated upto softening near the region of the opening and is pulled apart so as toproduce a reduction in cross-section of the opening and to facilitatethe subsequent process of sealingly melting or squeezing off. In aparticularly preferred embodiment the glass bulb already has a narrowedcross-section in the region of the further opening.

14. The pyrotechnic material may be cooled beforehand in order to avoidself-ignition. However, selecting a suitable distance between the regionto be heated and the pyrotechnic material may make the cooling of thepyrotechnic material unnecessary because of the low thermal conductivityof glass. The device thus produced comprises an integral glass housingwhich completely surrounds the pyrotechnic material and into which themetal ducts for the connecting cables of the igniter are melted in likein the known halogen bulbs. The device is therefore absolutely gas-tightand fluid-tight.

15. In a further embodiment of the method according to the invention,the spark gap or the heating wire is surrounded by at least part of thepyrotechnic material, for example in the form of a squib containing theprimary charge. The metal duct with the spark gap or the heating wireand the part of the pyrotechnic material surrounding the spark gap orthe heating wire is then introduced into a tubular glass bulb and theglass bulb is closed in the region of the metal duct in the manner asdescribed above. A self-ignition of the pyrotechnic material is avoidedpreferably by suitably selecting the distance between the pyrotechnicmaterial and the heated area of the opening. If required, additionalpyrotechnic material may be supplied to the glass bulb through a furtheropening and the opening may thereafter be closed by sealingly melting,pressing or squeezing, as described above.

16. It is furthermore possible to introduce first the pyrotechnicmaterial and thereafter the metal duct with the spark gap or the heatingwire into the glass bulb provided with an opening and then to close theopening in the region of the metal duct in the manner as describedabove. For this purpose, for example a glass bulb is provided, which isfilled with the pyrotechnic material. Then the metal ducts, equippedwith a heating wire or a spark gap, for the connecting cables areintroduced into the glass bulb. In this case as well, the heating wireor the spark gap can already be surrounded by a squib containing theprimary charge. Thereafter, the glass bulb containing the pyrotechnicmaterial may be cooled intensively by means of liquid air or liquidnitrogen and the glass bulb may be closed by melting. The cooling stepmay be dispensed with if a suitable distance is kept between thepyrotechnic material and the heated area. This method, too, ensures atotally gas-tight and fluid-tight connection of the components of theigniter according to the invention.

17. If an acceleration sensor arranged in a vehicle detects an accident,the igniter connected electrically with the sensor is activated. Thecurrent impulse originating from the sensor causes a burning through ofthe heating wire or the jumping of a spark in the spark gap. Thereby,the pyrotechnic material or preferably the primary charge surroundingthe heating wire is ignited. This primary charge in turn ignites thebooster charge contained in the glass bulb. The ignition of the primarycharge and/or of the booster charge causes a distinct pressure increaseto occur inside the glass bulb, which causes the latter to burst. Inthis way, the hot particles released by the burning of the boostercharge can strike onto a pyrotechnic propellant contained in the gasgenerator and can cause it to ignite.

18. The same mode of operation occurs if, instead of the igniter, thegas generator is constructed according to the invention with a glasshousing. In this case, the ignition of the pyrotechnic materialcontained in the gas generator causes a pressure increase which causesthe gas generator housing to burst. The hot gases produced by theburning of the pyrotechnic material are thus released and can actuatethe safety arrangement, for example a belt tensioner or airbag.

BRIEF DESCRIPTION OF THE DRAWINGS

19. Advantageous embodiments of the invention will be apparent from thefollowing description, in which reference is made to the encloseddrawings in which:

20.FIG. 1 is a diagrammatic view of an igniter according to theinvention;

21.FIG. 2 is a cross-sectional view of an igniter according to theinvention;

22.FIG. 3 shows a gas generator according to the invention;

23.FIG. 4 shows an igniter with an arrangement for exposing an opening;

24.FIG. 5 shows a gas generator with an arrangement for exposing anopening; and

25.FIG. 6 is a cross-sectional view of a gas generator with an igniteraccording to the invention.

DESCRIPTION OF PREFERRED EMBODIMENTS

26. The igniter shown in FIGS. 1 and 2 comprises a housing 10 of glass.Metal ducts 14 are melted into the glass bulb or glass housing 10 in agas-tight and fluid-tight manner. At the end of the metal ductsprojecting into the housing, a heating wire or a spark gap 16 isarranged. The heating wire or the spark gap 16 is surrounded by aprimary charge 18. In the housing in addition a booster charge 20 canalso be arranged, which receives and boosts the energy released by theprimary charge 18 in the case of activation of the igniter.

27. If the igniter is activated by a current impulse originating from anacceleration sensor (not shown here), the heating wire or the spark gap16 firstly ignites the primary charge 18 which in turn causes theburning of the booster charge 20. Through the burning of the boostercharge 20 and/or of the primary charge 18, a pressure increase occurs inthe housing 10. Through this pressure increase, the housing 10 burstsand releases the energy-rich, hot particles formed by the burning of thebooster charge.

28. The gas generator illustrated in FIG. 3 basically has the samestructure as the igniter shown in FIGS. 1 and 2. The housing 10 of thegas generator is likewise formed from glass. Metal ducts 14 are meltedinto the glass bulb or glass housing 10 in a gas-tight and fluid-tightmanner, which at their end projecting into the gas generator have aheating wire or a spark gap 16. The heating wire or the spark gap 16 aresurrounded by a squib 22 which can contain a primary charge and also inaddition a booster charge (not shown here). In addition a propellant 24is introduced into the glass housing 10 of the gas generator, theactivation of which propellant 24 leads to a bursting of the glasshousing 10 and hence to a release of the hot gases formed by the burningof the propellant 24. By means of these hot gases, a safety arrangement,for example a belt tensioner unit or an airbag module, can be actuated.

29.FIG. 4 shows an igniter which basically has the same structure as theigniter illustrated in FIGS. 1 and 2. In the embodiment illustratedhere, an opening 26 is provided in the igniter housing 10 formed fromglass, which opening 26 is closed by a sealing means 28. The sealingmeans 28 has the characteristic that with an action of heat from theexterior, below the self-ignition temperature of the pyrotechnicmaterial introduced into the igniter, for example of the primary charge18 or of the booster charge 20, it alters its structure, its physicalcondition or its volume and thereby exposes the opening 26. As sealingmeans, for example a low-melting-point metal alloy can be used. Theexposing of the opening ensures that the gases developing as a result ofa self-ignition of the pyrotechnic material can flow away in acontrolled manner.

30. The gas generator shown in FIG. 5 likewise has the opening 26provided in the housing 10 formed from glass. As described above, thisopening is closed by a sealing means 28, for example a low-melting-pointmetal alloy. The opening 26 or the sealing means 28 can be arranged atany desired point on the housing 10. It is also conceivable that athermal action from the exterior and the change to the structure, thephysical condition or the volume of the sealing means connectedtherewith, leads not only to an exposing of the opening 26 but also to apartial destruction of the housing 10. Thereby, the surface area of theopening available for the outflow of the gas produced as a result of theself-ignition of the propellant is enlarged. In the housing 10 also aplurality of openings 26, closed by the sealing means 28, can beprovided.

31. Finally, FIG. 6 shows an example for application of a gas generatorincluding an igniter according to the invention inserted in the gasgenerator. The gas generator illustrated here comprises a housing 30formed of conventional materials such as aluminum or steel and a basepart 32 closing off the housing. The base part may be made of plastic.In an upper portion of the base part 32 facing the interior of thehousing 30, an O-ring 34 is arranged which holds the housing 30 inposition in the nature of a latch. Further latching means may beprovided on the outer periphery of the base part 32 for holding thehousing in place.

32. Further, an igniter according to the invention is inserted in theupper part of the base part 32, between the O-ring 34. This igniter hasthe same structure as the igniter shown in FIGS. 1 and 2, i.e. itconsists of a housing 10 which is entirely formed from glass and hasmetal ducts 14 melted into it in a gas-tight and fluid-tight manner. Themetal ducts 14 comprise a heating wire 16 at their ends projecting intothe glass housing 10 of the igniter. The heating wire may also bereplaced by a spark gap in the known manner. The heating wire 16 issurrounded by a primary charge 18 which in turn is in contact with abooster charge 20. At their ends emerging from the glass housing 10 themetal ducts 14 are connected with the connecting cables 36 for theigniter.

33. The gas generator illustrated in FIG. 6 may be used in belttensioner units, for example. When the igniter is activated via theigniter connecting cables 36, the heating wire 16 will fuse and thusignite the pyrotechnic material 18, 20 contained in the glass housing 10of the igniter. The increase in pressure brought about by the burning ofthe pyrotechnic material 18, 20 causes the glass bulb of the igniter toburst and releases the housing 30 of the gas generator from its lockedposition. The displacement of the housing 30 may be transferred in aknown manner to a linear drive for a belt tensioner via a shoulder 38arranged on the outer periphery of the housing 30.

34. Use of the igniter illustrated here is however not limited to gasgenerators for belt tensioner units. Rather, the igniter according tothe invention may be utilized in any one of the known gas generators forsafety arrangements, for instance in gas generators for driver's sideimpact protective device, front passenger impact protective devices andside impact protective devices.

35. To produce the device according to the invention or the igniteraccording to the invention, preferably a glass tube is provided whichhas a first opening and a second opening located opposite the firstopening. The metal ducts, which preferably consist of tungsten or atungsten alloy, are then introduced into the glass tube through thefirst opening with the heating wire or forming a spark gap, and theglass tube is heated in the region of the first opening until the glasssoftens, and is pressed so as to melt the metal ducts into the glasstube in a gas-tight and fluid-tight manner. The glass tube including themetal ducts melted into it may also be provided as a prefabricatedcomponent, such as is known, for example, from the production of halogenbulbs.

36. When the glass tube or glass bulb containing the metal ducts hasbeen produced, the pyrotechnic material is introduced into the glassbulb through the second opening. The introduction of the pyrotechnicmaterial may be performed in a plurality of steps which may beinterrupted by drying stages. In this way it is also possible tointroduce different pyrotechnic materials and to make thecharacteristics of the device suitable for any specifically desiredpurpose of application. Finally, the glass bulb containing thepyrotechnic material is sealingly melted in the region of the secondopening. Preferably, the glass bulb already has a narrowed cross-sectionin this region, so that the step of sealingly melting may be effected byheating and pulling the glass bulb apart in the region of the narrowedcross-section. When proceeding in this manner, a cooling of theremaining portions of the glass bulb or of the pyrotechnic material maybe done without due to the poor thermal conductivity of glass.

37. The igniter according to the invention ensures that the pyrotechnicmaterial contained inside it is sealed in an absolutely gas-tight andfluid-tight manner and thus increases the functional reliability of theparticular gas generator or safety arrangement concerned. At the sametime, the application of a simplified and continuous manufacturingmethod allows a production of the igniter according to the invention ata favorable cost.

What is claimed is:
 1. A device containing a pyrotechnic material,comprising a housing surrounding the pyrotechnic material, wherein thehousing is formed entirely from glass, the housing containing at leastone metal duct comprising a spark gap or a heating wire.
 2. The deviceaccording to claim 1 , wherein the device is an igniter for a gasgenerator.
 3. The device according to claim 2 , wherein the heating wireor the spark gap is connected with the pyrotechnic material.
 4. Thedevice according to claim 2 , wherein the pyrotechnic material comprisesa primary charge and a booster charge.
 5. The device according to claim1 , wherein the device is a gas generator for a safety arrangement inmotor vehicles.
 6. The device according to claim 5 , wherein the safetyarrangement is a belt tensioner unit or an airbag module.
 7. The deviceaccording to claim 1 , wherein the pyrotechnic material is solid, liquidor gaseous.
 8. The device according to claim 1 , wherein the housing hasat least one opening which is closed by a sealing means, the sealingmeans altering its physical condition, its structure or its volume as aresult of an action of heat from the exterior below the self-ignitiontemperature of the pyrotechnic material in such a way that the openingis exposed.
 9. The device according to claim 8 , wherein the sealingmeans is a low-melting-point metal alloy or a liquid contained in aclosed glass container, the glass container being introduced into theopening.
 10. A method of manufacturing a device containing a pyrotechnicmaterial, wherein the method comprises the steps of: (a) providing aglass bulb having at least one opening; (b) introducing the pyrotechnicmaterial and at least one metal duct comprising a spark gap or a heatingwire into the glass bulb; (c) closing the opening of the glass bulbforming a glass housing completely surrounding the pyrotechnic materialand containing the metal duct comprising the spark gap or the heatingwire.
 11. The method according to claim 10 , wherein the glass bulb isheated in the region of the opening until the glass softens, and theopening is closed by sealingly melting or pressing.
 12. The methodaccording to claim 11 , wherein the pyrotechnic material is cooledduring heating.
 13. The method according to claim 11 , wherein theheated area of the glass bulb is arranged at a distance from thepyrotechnic material, the distance being selected such that a cooling ofthe pyrotechnic material may be dispensed with.
 14. The method accordingto claim 10 , wherein the glass bulb has a narrowed cross-section in theregion of the opening.
 15. The method according to claim 14 , whereinthe glass bulb is heated, pulled apart and sealingly melted in theregion of the narrowed cross-sectional portion.
 16. The method accordingto claim 10 , wherein prior to introducing the pyrotechnic material, themetal duct comprising the spark gap or the heating wire is introducedinto the glass bulb and the glass bulb is closed in the region of themetal duct.
 17. The method according to claim 10 , wherein at least partof the pyrotechnic material surrounds the spark gap or the heating wire,the metal duct comprising the spark gap or the heating wire and the partof the pyrotechnic material surrounding the spark gap or the heatingwire is introduced into the glass bulb and the glass bulb is closed inthe region of the metal duct.
 18. The method according to claim 10 ,wherein the pyrotechnic material is introduced into the glass bulb andwherein subsequently the metal duct comprising the spark gap or theheating wire is introduced into the glass bulb and the glass bulb isclosed in the region of the metal duct.
 19. The method according toclaim 10 , wherein the glass bulb is a glass tube having a first openingand a second opening located opposite the first opening, wherein themetal duct comprising the spark gap or the heating wire is introducedinto the glass tube through the first opening and the glass tube, in theregion of the first opening, is heated up to softening and closed andwherein subsequently the pyrotechnic material is introduced into theglass tube through the second opening and the glass tube, in the regionof the second opening, is heated up to softening and closed.
 20. Themethod according to claim 19 , wherein the narrowed cross-sectionalportion is arranged in the region of the second opening.
 21. The methodaccording to claim 19 , wherein the glass bulb obtainable by introducingthe metal ducts and closing the first opening is provided as aprefabricated component.
 22. The method according to claim 10 , whereinthe device containing the pyrotechnic material is an igniter in a gasgenerator for a safety arrangement in motor vehicles.